Feeling the need to test private methods is usually a sign that your code needs refactoring. The recommended approach is that you test your code via it’s public interface. Since your private methods are only accessible via those public methods, it goes that if you have thoroughly testing via the public interface, your private methods will have been tested too.

Still, there can be times testing private methods can be useful. For example, while dealing with either legacy code or when using it as a temporary step while refactoring.